Extracellular protein isolation

I have to isolate a bacterial extracellular protein which takes part in biofilm formation and adhesion so it is structural protein so we cannot do any enzyme assay to trace it.
I didnt get any proper protocol where i can isolate this Extracelluar protein exclusively, in some methods sonication was used and debris was seperated. protein content was isolated to show correlation between biofilm formation and protein content. the corresponding gene is 9 having kb lenght so overexpression and isolation with tag is tedious. So how sould I proceed ??
plz give me some ideas